RESULTS OF IMMUNOSCINTIGRAPHY USING A COCKTAIL OF RADIOLABELED MONOCLONAL-ANTIBODIES IN THE DETECTION OF COLORECTAL-CANCER

Background: External immunoscintigraphy using a single monoclonal anti body has been employed successfully to localize primary, recurrent, an d occult colorectal carcinoma. This prospective study investigated the accuracy and sensitivity of external immunoscintigraphy when the comb ination or ''cocktail'' of radiolabeled monoclonal antibodies, CYT-103 (an IgG la) and CYT-372 (an IgG2b) directed against TAG-72 and CEA, r espectively, is given to patients with known or suspected colorectal c ancer. Methods: Eleven patients enrolled in this open label phase I/II study underwent preoperative external immunoscintigraphy after intrav enous cocktail administration of two indium 111-labeled monoclonal ant ibodies (MoAb), CYT103 and CYT372. Antibody dose ranged from 0.2 mg (f ive patients) to 1.0 mg (six patients), each antibody radiolabeled wit h 2.5 mCi of indium ill, delivering a total dose of 5 mCi per patient. Planar and SPECT images were performed 2 to 5 days postinjection. Sus pected lesions were surgically resected within 2 weeks of injection. R esults: A total of 23 lesions (sites) were identified in the eleven pa tients, 19 of which were confirmed by pathology (hematoxylin and eosin [H&E]). Cocktail immunoscintigrams identified 16 of the 19 confirmed lesions. Computed tomography (CT) scan detected 9 of the 19 lesions. T he sensitivities of cocktail immunoscintigraphy and CT scan for the de tection of colorectal cancer were 84% and 64%, respectively. The posit ive predictive value for immunoscintigraphy was 94%. The antibody scan s detected six occult, previously unsuspected lesions. Cocktail immuno scintigraphy changed the surgical management in four of the 11 (36%) p atients. Conclusions: The combination of In 111 CYT-103 and CYT-372 im proved the sensitivity of external immunoscintigraphy for the detectio n of colorectal cancer compared to that obtained with a single MoAb im aging. Cocktail antibody imaging may enhance the staging and managemen t of patients with cancers of colon and rectum.